Spinach can carry more than a thousand milligrams of oxalate per 100 grams, and the compound does bind calcium and iron and feed kidney stones in people prone to them, but boiling leaches much of it out and cutting dietary calcium to fight stones backfires.
Vegan Brief·Evidence last reviewed August 22, 2026
This is a summary of the cited evidence, not medical advice.
Spinach, per 100 g330–2,350 mg total oxalate
Oxalate absorbed~5–10% under normal conditions
Stone formers vs. healthy9.2% vs. 6.7% oxalate absorption
01
The short version
Oxalate is a plant compound that grabs onto calcium, iron and other minerals in the gut, and it is the specific reason spinach and a handful of other plant foods get singled out as a health worry.
Primary source 01 / 10
Oxalic acid, or "oxalate," is a naturally occurring plant chemical which, in the human diet, can react with calcium, iron, and other minerals to inhibit mineral absorption. Foods such as tea, beets, rhubarb, strawberries, spinach, and chocolate are known to increase oxalate in the urine and may contribute to kidney stone formation.
USDA's own summary does not stop at the warning. It adds the other half of the picture in the very next line.
Primary source 02 / 10
Spinach in particular contains higher concentrations of oxalate than most crops, but it is also considered healthful because it is rich in a number of key nutrients.
What it binds, and how much actually gets absorbed
Spinach is the extreme case among common foods: a 2023 review put its published oxalate content across a huge range depending on variety and growing conditions.
Primary source 03 / 10
published oxalate values are 329.6–2350 mg total oxalates/100 g fresh weight (FW) for spinach
Eating oxalate alongside calcium or magnesium cuts that further, by the same binding mechanism that makes oxalate a mineral thief in the first place.
Primary source 05 / 10
a simultaneous consumption of oxalate with calcium or magnesium can reduce its bioavailability and absorption due to the formation and fecal excretion of insoluble salts, lowering the health risk
Absorption also is not fixed across people, and this is where the kidney-stone risk actually concentrates: in a subset of absorbers, not the general population.
Primary source 06 / 10
intestinal absorption of oxalates in individuals with a history of stone formation was expressly higher than in healthy individuals (9.2% and 6.7%, respectively)
boiling, steaming, soaking, and processing with calcium sources are some procedures to reduce the content of soluble oxalates, the most harmful oxalates
The kidney-stone question, and why cutting calcium backfires
For anyone who has actually had a calcium oxalate stone, NIDDK's own patient guidance runs against the intuitive fix.
Primary source 09 / 10
Even though calcium sounds like it would be the cause of calcium stones, it’s not. In the right amounts, calcium can block other substances in the digestive tract that may cause stones.
Its practical advice leans on swapping meat protein for legumes rather than avoiding oxalate-containing plants outright.
Primary source 10 / 10
Consider replacing some of the meat and animal protein you would typically eat with beans, dried peas, and lentils, which are plant-based foods that are high in protein and low in oxalate.
None of this is medical advice, and NIDDK repeats that point in its own guidance: anyone with a history of stones should work out sodium, calcium, protein and oxalate targets with a health care professional or dietitian, since the right diet differs by stone type. For most people who have never had a stone, oxalate is one input into a mineral supply chain that a varied diet, some cooking, and ordinary calcium intake already manage well.
Plant-based diets, gout and kidney stonesFor gout and kidney stones, cutting meat is one of the cleaner wins in nutrition. Vegetarians formed about a third fewer stones, and plant purines never earned their bad reputation.
What are phytates? How they affect iron and zinc absorptionPhytates, phosphorus's storage form in beans and grains, chelate iron, zinc and calcium and measurably cut how much a vegetarian diet absorbs, but soaking, sprouting and fermenting the same foods strip out most of it, and clinical trials also credit phytate with cutting kidney stones and slowing bone loss.
Does eating oxalate-rich food cause kidney stones?
It is one factor among several, and it matters most for people who already absorb oxalate at a higher rate. A 2023 review found stone formers absorbed about 9.2% of dietary oxalate versus 6.7% in healthy people, with most people absorbing only 5 to 10% under normal conditions.
Should I stop eating spinach or nuts to avoid kidney stones?
NIDDK's guidance does not call for eliminating oxalate broadly. Cooking methods such as boiling reduce soluble oxalate substantially, and pairing oxalate-containing foods with calcium reduces how much is absorbed. Anyone who has had a stone should get personalized guidance from a health care professional.
Does cutting calcium prevent kidney stones?
No. NIDDK's own guidance says the opposite: getting enough calcium from food helps block oxalate absorption in the gut, and too little dietary calcium can raise stone risk rather than lower it.
The primary sources
The documents this page quotes. Read them yourself.
Eating, Diet, & Nutrition for Kidney Stones · National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), 2017 · US-government patient guidance, last reviewed May 2017
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